Synthesis of nanopeapods by galvanic displacement of segmented nanowires

ABSTRACT

A method for fabricating nanostructures, which includes the steps of forming a multi-segmented nanowire; and performing a galvanic displacement reaction on the multi-segmented nanowire. The method utilizes template directed electrodeposition to fabricate nanowires with alternating layers of sacrificial/noble metal, enabling a new level of control over particle spacing, aspect ratio, and composition. Moreover, by exploiting the redox potential dependent reaction of galvanic displacement, nanopeapod materials can be extended (semiconductor/metal, p-type/n-type, metal/metal, ferromagnetic/nonmagnetic, etc.) beyond the fundamental metal/metal-oxide nanopeapods synthesized by high temperature techniques. In accordance with an exemplary embodiment. Co/Au and Ni/Au multisegmented nanowires were used to create Te/Au nanopeapods by galvanic displacement, producing Te nanotubes and nanowires with embedded Au particles, respectively.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application claims priority to U.S. Provisional PatentApplication Ser. No. 61/347,212, filed May 21, 2010, which isincorporated herein by reference in its entirety.

FIELD OF THE INVENTION

This invention relates to a method and system of synthesizingnanopeapods by galvanic displacement of segmented nanowires, and moreparticularly to a method and system of fabricating nanostructures byforming a multi-segmented nanowire with alternating layers ofsacrificial/noble metals, and performing a galvanic displacementreaction on the multi-segmented nanowire.

BACKGROUND

Nanoengineered materials utilize diminutive features to enhanceinterface/surface properties and overcome limitation of conventionalmaterials. In recent years, progress in this field has been directedtowards the fabrication of complex layered nanostructures such ascore/shell configurations and advanced assembly techniques forfunctional arrangements of nanoparticles. Both of these routes, whilepromising, are in the nascent stages of development largely due to thehigh level of accuracy and localization required when modulatingcomposition or aligning nanomaterials. One unique structure that hasrecently emerged with demonstrated enhancement of optoelectronicproperties and promise as precisely fabricated linear assemblages ofnanoparticles for plasmon waveguides are nanoparticle embedded nanotubesor nanopeapods.

To date, nanopeapods have been fabricated by a limited number oftechniques typically requiring either a microwave reactor or ananoporous template. The former is a specific, complex method withstringent conditions and a solid husk with little evidence fordimensional control over the sheathing material or material variation.Of the template techniques there are three different approaches thathave demonstrated feasibility in terms of material selection anddimensional control. The first method utilizes a template to fabricatemultisegmented nanowires, which are subsequently coated by a nanometerthin porous silica shell using sol gel chemistry. The nanowire consistsof alternating layers of noble/base metals (i.e. Au/Ni, Ag/Ni) allowingthe more base metal to be chemically etched after the silica coating.The nanoparticle chain materials and dimensions for this process can befinely tuned since they are determined by electrodeposition of the metalsegments and template pore size. The second approach employs ananoporous alumina template or a nanowire as a template for atomic layerdeposition (ALD). This process requires ALD of two metal oxide (orpolymer) materials, an outer shell and inner sacrificial layer. In thecase of the metal oxide template, metal nanowires are thenelectrodeposited into the double coated nanopores. After etching thetemplate and sacrificial layer the intermediate structure, composed of ametal oxide nanotube partially filled with a metal nanowire, emerges. Todelineate the metal nanowire into particles or rods, one can takeadvantage of the Rayleigh instabilities during the annealing process.The procedure is more general with greater material variety of the shell(metal oxides or polymer). The last technique also relies onelectrodeposition to generate base/noble metal multilayered nanowireswithin an alumina template, but solid state reaction differentiatestheir approach from others. The solid state reaction creates a new tubematerial by diffusion of the base metal into the alumina template, whereKirkendall effects create the void spaces between the noblenanoparticles.

However, all of the previously described methodologies suffer from onecommon limitation; the inability to fabricate nanoparticle and shellstructures from materials such as metal/semiconductor, p-type/n-typesemiconductor, metal/metal, metal oxide/metal oxide, orferromagnetic/nonmagnetic. Accordingly, it would be desirable tofabricate nanoparticle and shell structures from materials such asmetal/semiconductor, p-type/n-type semiconductor, metal/metal, metaloxide/metal oxide, or ferromagnetic/nonmagnetic and introduce thesefabricated nanoparticles and shell structures into a host offundamentally important studies with applicability to thermoelectricmaterials, spintronics, nanosensors, and plasmonics. Additionally, itwould be desirable to modulate nanowire/nanotube structures of the samecomposition offer an efficient route to study confinement effects withinnanotubes.

SUMMARY

In accordance with an exemplary embodiment, a facile technique tofabricate one-dimensional semiconductor nanostructures with preciselypositioned embedded metal nanoparticles, termed nanopeapods, isdisclosed herein. These engineered nanostructures have demonstratedenhanced photosensitivity in previous reports and have projectedapplication as plasmon waveguides. One of the novel aspects of thisprocess is the use of electrodeposited multi-segmented nanowires withgalvanic displacement reaction to create such nanopeapods. This approachutilizes template directed electrodeposition to fabricate nanowires withalternating layers of sacrificial/noble metal, enabling a new level ofcontrol over particle spacing, aspect ratio, and composition. Moreover,by exploiting the redox potential dependent reaction of galvanicdisplacement, nanopeapod materials can be extended (semiconductor/metal,p-type/n-type, metal/metal, ferromagnetic/nonmagnetic, etc.) beyond thefundamental metal/metal-oxide nanopeapods synthesized by hightemperature techniques. In accordance with an exemplary embodiment.Co/Au and Ni/Au multisegmented nanowires were used to create Te/Aunanopeapods by galvanic displacement, producing Te nanotubes andnanowires with embedded Au particles, respectively. It can beappreciated that different nanowire diameters and segment lengths areembodied, which demonstrates nanoscale precision

In accordance with an exemplary embodiment, a method for fabricatingnanostructures, comprises the steps of: forming a multi-segmentednanowire; and performing a galvanic displacement reaction on themulti-segmented nanowire.

In accordance with another exemplary embodiment, a nanostructureproduced by the process of forming a multi-segmented nanowire andperforming a galvanic displacement reaction on the multi-segmentednanowire.

The details of one or more embodiments of the disclosure are set forthin the accompanying drawings and the description below. Other features,objects, and advantages will be apparent from the description anddrawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention. In the drawings,

FIG. 1 shows a schematic of galvanic displacement reaction progressionfor Co/Au multisegmented nanowires, wherein (A) shows the as synthesizedCo/Au (Cobalt/Gold) nanowire is (B) sheathed in a thin porous Te(Tellurium) coating (C) that permits continued dissolution of the Cosegments as the Te coating continues to grow, (D) until the Te tube withembedded Au particles is all that remains.

FIG. 2 shows SEM (scanning electron microscope) images of (A)electrodeposited Co/Au multisegmented nanowires and (B, C) thecorresponding Au/Te nanopeapod structure synthesized by galvanicdisplacement, and wherein (D) the EDX spectrum of image (C) indicatesthe presence of Te and no detectable concentration of Co, and additionalpeaks pertain to the Au segments, 2.12 keV, and substrate materials, Cu8.04 keV and Al 1.48 keV.

FIG. 3 shows TEM (transmission electron microscopy) images of (A-B)Co/Au multisegmented nanowires and (C-D) Te/Au nanopeapods, and whereinEDX (Energy-dispersive X-ray spectroscopy) and SAED (Selected area(electron) diffraction) patterns for Co/Au nanowires (E-F) before andafter (G-H) galvanic displacement are also shown, and wherein scale barsare as follows: 20 nm and 200 nm for (C) and (A, B, D), respectively.

FIG. 4 shows TEM images of Au/Te nanopeapods produced from a 30 nmpolycarbonate template.

FIG. 5 shows SEM images of Ni/Au nanowires fabricated from (A) 200 nmalumina templates and (C) 30 nm polycarbonate membranes, and wherein thecoated structures after galvanic displacement are shown in (B) and (D)for alumina and polycarbonate, respectively, and the insets of (A-B) areEDX patterns for their corresponding images, (E-F) SEM images of (E) 200nm Ni/Au and (F) 50 nm galvanically displaced Ni/Au nanowires withdifferent segment lengths, and wherein scale bars are as follows: (A) 10μm, (B-C, E) 5 μm, (D) 1 μm, and (F) 0.2 μm.

FIG. 6 shows (A-B) Darkfield and (C-D) brightfield TEM images of Ni/Aunanowires, wherein (A) the EDX line scan confirms segment contrast for(red) Ni and (blue) Au, (D) the brightfield TEM images corresponds tothe (E-F) SAED patterns below, and wherein the scale bars are asfollows: (A) 1 μm, (C) 0.5 μm, and (B, D) 0.1 μm.

FIG. 7 shows (A-F) Brightfield TEM images of Ni/Au multisegmentednanowires synthesized from a 50 nm polycarbonate template after galvanicdisplacement, the boxes in (C) correspond to the images in (D-F) andSAED patterns in (G-I), and the SAED patterns (J), (K), and (L) are theexact same SAED patterns as (G), (H), and (I), respectively, withnumbered spots and corresponding white rings for d-spacing values inTable 2 and 3, and wherein the scale bars are as follows: (A-B) 100 nm,(C) 10 nm, and (D-F) 2 nm.

FIG. 8 shows (A-C) Darkfield TEM images of Ni/Au nanowires fabricatedwith 50 nm polycarbonate templates and subjected to galvanicdisplacement reaction with Te, and wherein the box in (C) indicates thearea of the EDX mapping for (D) Te, (E) Au, and (F) Ni, and whereinscale bars are as follows: (A) 0.2 μm, (B) 20 nm, and (C) 400 nm.

FIG. 9 shows (A-E) Brightfield TEM images of Ni/Au multisegmentednanowires from 30 nm polycarbonate template after galvanic displacement,and wherein the boxes in (A) correspond to the images in (B-E) and SAEDpatterns in (F-K), the SAED patterns (I), (J), and (K) are the exactsame SAED patterns as (F), (G), and (H) respectively, with numberedspots and corresponding white rings for d-spacing values from Tables 4and 5, and wherein the scale bars are as follows: (A) 10 nm and (B-E) 2nm.

DETAILED DESCRIPTION

In accordance with an exemplary embodiment, a system and method ofgalvanic displacement of electrodeposited multisegmented nanowires canbe obtained as a simple and scalable method to achieve such nanopeapodstructures. This procedure utilizes template directed electrodepositionto fabricate multilayer nanowires, providing the spacing precision ofelectrodeposition. Since no heat treatment is required for this process,the embedded particles can range from very thin discs to nanorods.Additionally, it can be appreciated that more exotic nanopeapodmaterials are feasible (oxidizable metals, semiconductors, etc.) forgalvanic displacement reaction, which depends on half reactionpotentials of the nanowire segments and material to be deposited.

In accordance with an exemplary embodiment, Te (Tellurium) nanotubeswith embedded Au (Gold) nanoparticles and Te nanowires with embedded Aunanoparticles were fabricated by galvanic displacement reactions. Inaccordance with an exemplary embodiment, the procedure for fabricatingnanopeapods follows that previously described for synthesizing Bi₂Te₃nanotubes, but utilizes a segmented sacrificial wire with an alternatingsequence containing a base element for displacement and a more nobleelement that remains after the displacement reaction. The segmentednanowires were synthesized by template directed electrodeposition, amethod pioneered by Martin and Moskovitz, which uses a nanoporoustemplate to confine electrodeposited material radially and thedeposition condition to control the axial length of the nanowire. Tostart, alumina (Whatman Anodisk 13) templates and polycarbonatemembranes (Nucleopore 30 nm and 50 nm) were sputtered with Au on oneside using an EMS KX550 sputter coater. It can be appreciated that thesputtered Au acts as a seed layer for electrodeposition to proceed upon.In accordance with an exemplary embodiment, alternating layers of Co/Auand Ni/Au can be electrodeposited as a dual bath method at differentdiameters and lengths. After electrodeposition the nanowires wereharvested using 1M NaOH at room temperature to etch alumina templatesand 1-methyl-2-pyrrolidinone at 50° C. to dissolve polycarbonatemembranes for eight hours each. The nanowires were washed three times bycentrifuging or settling, extracting the solvent and the addition ofnanopure water (Millipore A). Portions of nanowire batches weresuccessively transferred to isopropyl alcohol (IPA) by a similarsequence of washings.

In accordance with an exemplary embodiment, nanowire electrodepositionswere carried out in 100 mL electrochemical cells with a three electrodeconfiguration using a saturated calomel electrode (SCE) as a referenceelectrode. The Cobalt (Co) electrolyte consisted of 1.0M CoCl₂+1.0MCaCl₂ at a pH of 4.0. Cobalt (Co) electrodeposition was performedgalvanostatically, −10 mA/cm², and potentiostatically, −0.96V (vs. SCE),at room temperature with no agitation. The Au segments wereelectrodeposited from a sulfite-based commercial Technic bath, 25RTU-ES, containing 40 mM of Au at a potential of −0.5V (vs. SCE) or acurrent density of -1 mA/cm² and a temperature of 50° C. with agitationfrom a 1 inch stir bar at 300 revolutions per minute.

Synthesis of Ni/Au nanowires followed the same protocol as that of Co/Aunanowire synthesis. The Co electrolyte was simply substituted with a Nielectrodeposition bath. The composition of the bath was 1.5MNi(NO₂SO₃)₂+0.4M H₃BO₃+0.2M NiCl₂ at pH 4.0. H₃BO₃ was added as a bufferand NiCl₂ was used to enhance anode dissolution. Ni was electrodepositedgalvanostatically at -10 mA/cm² in a two electrode configuration with aNi counter electrode for alumina templates and potentiostatically in athree electrode configuration at -0.96 vs. SCE for polycarbonatetemplates.

Galvanic displacement reactions were performed on both substrate boundnanowires and suspended nanowires. The substrate bound nanowiresemployed Co/Au and Ni/Au multisegmented nanowires suspended in IPA, asthe solvent evaporated quickly and provided good nanowire dispersion.The nanowires were cast on Si substrates (0.25 cm²) and allowed to dry.The substrate bound nanowires were then submerged in 10 μL of the nitricacid Te solution, 1M HNO₃+10 mM TeO₂, for 30 minutes. Following thedisplacement reaction, the solution was carefully wicked with a KimWipeand washed with a sequence of 10 μL droplet of nanopure water on thesubstrate and wicking, three times each. Nanowires suspended in nanopurewater were used for galvanic displacement in solution. 10 μL of thenanowire suspension was drawn and then dispensed in 1 ml of the Tesolution. The nanowires were immediately shaken to prevent agitation andto set aside for 30 minutes before washing three times with nanopurewater. SEM micrographs were taken with a Phillips XL30 FEG SEM and LEOSupra 55 SEM. TEM micrographs were taken on C coated Cu grids with a FEIPhillips CM300 TEM.

It can be appreciated that galvanic displacement reaction has beenpreviously utilized to create a wide variety of metal nanoshells ornanostructures with hollow interiors. This process was later adopted toyield multi-walled metal nanoshells with shells of different metalcomposition. It can be appreciated that galvanic displacement reactionshas been extended to generate semiconductor and compound semiconductornanotubes from ferromagnetic nanowires. However, to date galvanicdisplacement has not been implemented with segmented bimetallicnanowires or to create metal/semiconductor nanostructures, wherein onemetal component is displaced by a semiconductor material and the otheris retained. Thus, methodical incorporation of semiconductornanomaterials with prearranged bimetallic nanowires is a critical step,drastically augmenting the utility of galvanic displacement ofnanostructures.

The driving force for galvanic displacement reactions is the differencein redox potentials, a fundamental electrochemical process. Themechanism for creating hollow nanostructure by galvanic displacementreactions starts with particle nucleation and growth of the more noblematerial on the surface of the sacrificial metal nanostructure, forminga thin, porous sheath. As the shell fills in, diffusion across thecasing allows for continued oxidation/dissolution of the sacrificialmetal. The end result is a hollow nanostructure with an interior roughlyresembling the exterior of the sacrificial metal.

The procedure, as applied to the Co/Au multilayered nanowire system, isshown in FIG. 1. In these experiments Te coats the Au segments as itencapsulated the volume of the pre-existing Co segment. This feature isa result of the difference in electrode potentials of each metal in thebimetallic nanowire. As a consequence, Co/Au bilayers also behave asconjoined electrodes of an electrochemical cell, with Au as a cathodefor Te deposition and Co as the dissolving anode. SEM images of theCo/Au nanowires and the Au particle embedded Te nanotube are shown inFIGS. 2A and 2B. The segments of the Co/Au nanowire are shown to beapproximately 2 μm and approximately 1 μm, respectively. A distinctchange in morphology after displacement indicates the entire structurehas been coated. The rough surface of the Te tube with the globularappearance at high magnification in FIG. 2C may be a consequence ofsurface roughness from the Co oxide layer or even the initial porositythat is enables continued dissolution of the Co across the Te shell.However, similar morphological coatings on the Au segments suggest itmay also be a result of the growth mechanism, which is likely due to lownucleation and surface mobility, typical factors causing botryoidaldeposits. It can be appreciated that in accordance with an exemplaryembodiment, by increasing the temperature it may provide a means toimprove crystallinity. The transparency of the Te allows the Au segmentsto be visually located with SEM and reveals a fairly consistent outerdiameter for the Te nanotube, especially for coatings over the Ausegments. The displacement of Co by Te after the galvanic displacementreaction was verified by energy dispersive X-ray spectroscopy (EDX). TheEDX spectrum in FIG. 2D clearly indicates the absence of Co and theappearance of Te.

The TEM images in FIG. 3 reveal the solid wire and tube cross section.The Co/Au nanowires can be clearly differentiated in FIG. 3B, with theCo segments approximately 2 μm in length and the Au segments, darker incolor, are approximately (˜) 1 μm in length. The thick, fragmented oxidelayer on Co gives the appearance of a hairy nanowire. The enlarged imagethe Te tube segment, after displacement, reveals the granular structure,with small grains. The structure of the Te coating was verified byselected area diffraction pattern (FIG. 3C inset), revealing apolycrystalline structure in agreement with similar results. Althoughpolycrystalline in nature, previous demonstrations of refluxing atelevated temperatures may improve the crystallinity, in accord with theobserved microstructure. Additionally, the wall thickness ranges fromapproximately 10 nm to approximately 27 nm with an inner diameter ofapproximately 225 nm to approximately 250 nm. It can be appreciated thatin accordance with an exemplary embodiment, the variation in tubediameter may be attributed to poor Co/Au interfaces, likely due tooxidation between depositions as a result of rinsing with water, oruneven Co surfaces due to template imperfections. It can be appreciatedthat interfacial quality can be ameliorated by selection of an acid Aubath or a single bath with pulsed electrodeposition.

In accordance with another exemplary embodiment, smaller Au/Tenanopeapod structures can also be fabricated from polycarbonatetemplates. Although the nominal pore size of these templates was 30 nmthe Au segments are shown to have a diameter of approximately 65 nm. Thewall thickness of the Te tube in FIG. 4A is measured to be approximately12.5 nm with an outer diameter of 75 nm, indicating a slightcontractions from the original Co segment diameter. It can beappreciated that this contraction is likely a consequence of the largeraspect ratio of the sacrificial Co segment, which is double that of thealumina template Co segment, permitting slight tube collapse prior tofilling in. The decrease in wall thickness from the larger diameterTe/Au nanopeapod is in accord with the reduced volume of the sacrificialCo. Additionally, the Te tube has a much more pronounced botryoidalmicrostructure, which also appears on the Au segment.

In contrast to Co/Au, Ni/Au multisegmented nanowires produced distinctlydifferent nanopeapods. It can be appreciated that the mechanisticnanopeapod formation described in FIG. 1 does not apply to nanopeapodsformed from Ni/Au nanowires. The structure of these nanopeapods is a Tenanowire with embedded Au segments. The mechanism for nanowire, asopposed to a tube (or tubular structure), formation between Au segmentsis likely due to the more positive electrode potential of Ni, withrespect to Co, slowing down the displacement kinetics and reducingelectron transfer between the bimetallic Ni/Au electrode junctions. Thisshift in potential can also provide kinetic favorability for etching ordisplacement along grain boundaries, which would allow progressivecontraction of the Te deposit as the Ni is displaced.

Representative SEM images of the Ni/Au multisegmented nanowires areshown in FIG. 5. Numerous variations of the Ni and Au segment lengthswere investigated for both alumina and polycarbonate templates. EDXanalysis of Ni/Au nanowires before galvanic displacement in FIG. 5Aindicate strong peaks for both elements. After galvanic displacement,FIG. 5B, the Ni peak is drastically reduced and Te appears. AdditionalNi/Au nanowires with different diameter and segment lengths are shown inFIGS. 5B-5D. TEM images with EDX line scans and selected area electrondiffraction patterns of 200 nm Ni/Au nanowires are shown in FIG. 6. TheEDX line scan clearly shows the delineation of the segments. In FIG. 6Ba compromised interface, presumable resulting from Au electrodepositionon Ni, is shown. This weaker junction alternates, as shown by the inset,with every other interface, consistent with pH induced oxidation oretching of Ni during Au electrodeposition. The SAED patterns of a singlenanowire and selected area show the polycrystalline structure of theAu/Ni segments, consistent with previous reports of Ni and Au nanowireselectrodeposited from a sulfamate and sulfite bath, respectively. Thecorresponding d-spacing values and orientations for FIG. 6F are shown inTable 1. The Au segments have plane spacings of (100), (200) and (422)with unit cell edge lengths, calculated for Au as a face centered cubicstructure, of 3.810, 4.092, and 4.025 Å, respectively. These values arereasonably close to the JCPDS value of 4.0786 Å. The Ni plane spacingsappearing from the SAED patterns are (111), (200), (220), (311), and(440), with a=3.527, 3.564, 3.623, 3.588, and 3.568 Å, which also lieclose to the literature value a=3.5238 Å.

TEM results for galvanic displacement reaction of Ni/Au nanowires grownfrom 50 nm polycarbonate templates are shown to be approximately 115 nmin diameter (FIG. 7). The Ni appears to be etched to near completionbeing replaced with granular Te segments. Lattice fringes from highmagnification TEM images of the Te/Au interface reveal the Te granulesto be as large as 6 nm. SAED patterns suggest a mixedpolycrystalline/amorphous structure and small grain sizes for the Tesegment with d-spacings for FIG. 7L shown in FIG. 7I and given by Table2 with their respective a values. The large deviation in a, given in Åin all tables, from the literature value of 4.4579 Å suggestsconsiderable defects or impurities and is confirms the suspected partialamorphous structure. The gold segments display a predominatelypolycrystalline structure with larger grains relative to Te, as depictedby FIGS. 7H-71. Contrary to larger Ni/Au multisegmented nanowires, thesesamples displayed minimal Te deposition on the Au segments. However, theTe top-coat may have contributed to the stronger deviations in a valuesfrom those reported for as synthesized Ni/Au nanowires (Table 3).Darkfield images of these nanowires also highlight the granularstructure of the Te segments and lack of tubular structure (FIG. 8). TheEDX area scans of one such Te segment depicts that Te is uniformlymapped over all segments along with Ni (Nickel). The high concentrationof Ni, Ni_(0.441)Te_(0.559) by EDX, is an important factor contributingto the plane spacing deviations and suggest the formation ofintermetallic NiTe, which is thermodynamically more favorable to Ni andTe (FIGS. 8D-8F). The corresponding NiTe planes and a values for FIG. 81are shown in Table 4. Some d-spacing values produce better lattice edgelength fittings to NiTe (a=3.9293 Å) than Te.

The TEM images for nanowires fabricated from 30 nm polycarbonatemembranes show the actual nanowire diameter to be approximately (˜) 75nm. The Te/Au interface of a Ni/Au nanowire subjected to galvanicdisplacement reaction is shown in FIG. 9. These wires appear verysimilar to those fabricated from 50 nm polycarbonate membranes. The highmagnification TEM images show a granular structure for the Te but withcomparably smaller and less lattice fringes, which agrees with thenearly amorphous SAED pattern. The Te coating on the Au is also morepronounced on these wires with thickness from 2-6 nm. Although the SAEDpattern is nearly amorphous, two points are distinguishable and havebeen assigned planes of (200) with very good lattice edge lengthfittings to both Te and NiTe (Table 5 and 6), however the intensityvalues for the NiTe plane spacing is much stronger than the Te. Thissupports the possibility of NiTe intermetallic formation, but isdifficult to confirm by SAED pattern alone. The SAED pattern for the Ausegments on these nanowires is similar to that of the previous nanowire,with good fitting lattice edge values except for a couple spots that canbe attributed to the Te coating (Table 7).

In accordance with another embodiment, a different approach wasinvestigated for the synthesis of nanopeapods, with one materialdiscontinuously embedded within the core of a different material. Thistechnique utilized template directed electrodeposition to fabricate amultisegmented nanowire of Co/Au, where Co serves as the sacrificialmetal for galvanic displacement and Au becomes encapsulated by the Tecoating. The Te coating over the Au was attributed to the difference inelectrode potentials of the Co and Au, allowing Au to mediate chargetransfer from Co to HTeO₂ ⁺. The displacement reaction was demonstratedwith both alumina and polycarbonate template fabricated nanowires. SEMimages revealed a botryoidal microstructure, which was also shown by TEMand attributed to low nucleation and surface mobility. The wallthickness of the nanopeapods was dependent on the quantity ofsacrificial Co, decreasing from approximately 20 nm to approximately12.5 nm as the initial diameter of the sacrificial Co segments decreasedfrom 225 nm to 65 nm. The smaller diameter nanopeapods exhibited slightcontraction of their tube segments, probably resulting from theincreased aspect ratio. Utilizing Ni sacrificial segments in a Ni/Aubilayer nanowire configuration produced Te nanowires with embedded Ausegments. The different structure was attributed to the difference inelectrode potentials of Co and Ni. Furthermore, EDX and SAED patternssupported intermetallic NiTe formation as opposed to elemental Te.Finally, this approach is believed to be a more general route tonanopeapod synthesis as numerous template directed electrodepositionmaterials can be incorporated, including conducting polymers, magneticmaterials, metal oxides, and compound semiconductors.

It will be understood that the foregoing description is of the preferredembodiments, and is, therefore, merely representative of the article andmethods of manufacturing the same. It can be appreciated that manyvariations and modifications of the different embodiments in light ofthe above teachings will be readily apparent to those skilled in theart. Accordingly, the exemplary embodiments, as well as alternativeembodiments, may be made without departing from the spirit and scope ofthe articles and methods as set forth in the attached claims.

TABLE 1 D-spacing values for the numbered spots from FIG. 6 (F) andcorresponding element, plane, and unit cell edge length (a). d-spacingSpot (nm) Element Plane a 1 0.3818 Au 100 3.818 2 0.6116 Ni 111 3.527 30.2046 Au 200 4.092 4 0.1782 Ni 200 3.564 5 0.1281 Ni 220 3.623 6 0.1082Ni 311 3.588 7 0.08216 Au 422 4.025 8 0.06308 Ni 440 3.568

TABLE 2 D-spacing, plane and unit cell edge length for Te from FIG. 7(I, L). d-spacing Spot (nm) Plane a 1 0.2795 101 3.659883 2 0.2792 1013.654834 3 0.2148 111 4.609348 4 0.1947 003 0 5 0.1605 202 4.409229 60.1211 114 4.203072 7 0.1138 105 4.693809

TABLE 3 D-spacing, plane and unit cell edge length for Au from FIG. 8(H, K). d-spacing Spot (nm) Plane a 8 0.2657 111 4.600 9 0.1926 2003.852 10 0.1348 220 3.812 11 0.1191 222 4.126 12 0.09891 331 4.311 130.09266 420 4.146 14 0.08230 422 4.032 15 0.07045 440 3.988

TABLE 4 D-spacing, plane and unit cell edge length for NiTe from FIG. 8(I, L). d-spacing Spot (nm) Plane a 1 0.2795 101 3.780839 2 0.2792 1013.775273 3 0.2148 102 4.139732 4 0.1947 110 3.894 5 0.1605 201 3.8844386 0.1211 203 3.800304 7 0.1138 300 3.942148

TABLE 5 D-spacing, plane and unit cell edge length for Te from FIG. 10(I). d-spacing Spot (nm) Plane a 21 0.1940 200 4.4802 22 0.1943 2004.4871

TABLE 6 D-spacing, plane and unit cell edge length for NiTe from FIG. 10(I). d-spacing Spot (nm) Plane a 21 0.1940 110 3.88 22 0.1943 110 3.886

TABLE 7 D-spacing, plane and unit cell edge length for Au from FIG. 10(K). d-spacing Spot (nm) Plane a 13 0.2304 111 3.990 14 0.2099 200 4.19815 0.1932 200 3.864 16 0.1422 220 4.022 17 0.1252 311 4.152 18 0.09215420 4.121 19 0.06839 440 3.868 20 0.05749 444 3.983

What is claimed is:
 1. A method for fabricating nanostructures, themethod comprising: forming a multi-segmented nanowire, wherein themulti-segmented nanowire includes alternating layers of sacrificial andnoble metals; dissolving the sacrificial metal by a galvanicdisplacement reaction on the multi-segmented nanowire in a tellurium(Te) solution; and thereby forming a tellurium (Te) tube with embeddednoble metals, wherein the embedded noble metals are in a spaced apartrelationship within a coating of tellurium, wherein the coating oftellurium coats the embedded noble metals and encapsulates at least avolume of the sacrificial metal, which has been dissolved.
 2. The methodof claim 1, comprising: forming the multi-segmented nanowire by templatedirected electrodeposition.
 3. The method of claim 1, wherein themulti-segmented nanowire is comprised of alternating layers of Co(Cobalt) and Au (Gold; and thereby forming a tellurium nanotube withembedded gold layers.
 4. The method of claim 1, wherein themulti-segmented nanowire is comprised of alternating layers of Ni(Nickel) and Au (Gold); and thereby forming a tellurium nanowire withembedded gold layers.
 5. The method of claim 1, comprising: performingthe galvanic displacement reaction on the multi-segmented nanowire,which is a substrate bound nanowire.
 6. The method of claim 1,comprising: suspending the multi-segmented nanowire in isopropyl alcohol(IPA) to provide dispersion; and submerging the multi-segmented nanowirein the tellurium (Te) solution.
 7. The method of claim 6, wherein themulti-segmented nanowire is comprised of alternating layers of Co(Cobalt) and Au (Gold), and the Co serves as the sacrificial metal forgalvanic displacement and the Au (Gold) becomes encapsulated by thetellurium coating.
 8. The method of claim 1, comprising: performing thegalvanic displacement reaction on the multi-segmented nanowire, which isa suspended nanowire.
 9. The method of claim 8, wherein the suspendednanowire is suspended in water and then dispersed in the tellurium (Te)solution.
 10. The method of claim 9, wherein the multi-segmentednanowire is comprised of alternating layers of Co (cobalt) and Au(gold), and the Co serves as the sacrificial metal for the galvanicdisplacement reaction and the Au becomes encapsulated by the tellurium(Te) coating.
 11. A method for fabricating nanostructures, the methodcomprising: forming a multi-segmented nanowire, wherein themulti-segmented nanowire includes alternating segments of a sacrificialmetal and gold nanoparticles; performing a galvanic displacementreaction in a tellurium (Te) solution on the multi-segmented nanowire todisplace the sacrificial metal; and thereby forming a tube of thetellurium with embedded gold nanoparticles, and wherein the embeddedgold nanoparticles are in a spaced apart relationship within a coatingof tellurium, and wherein the coating of tellurium coats the embeddedgold nanoparticles and encapsulates at least a volume of the sacrificialmetal, which has been dissolved.
 12. The method of claim 11, wherein thesacrificial metal is cobalt (Co) or nickel (Ni).
 13. The method of claim11, comprising: performing the galvanic displacement reaction on themulti-segmented nanowire, which is a suspended nanowire; and wherein thesuspended nanowire is suspended in water and then dispersed in thetellurium (Te) solution.